Due to the trend towards higher bandwidth demand and advances in the Wavelength Division Multiplexing, WDM, device technology, the WDM Passive Optical Network, PON, is considered as a possible candidate for next-generation broadband access networks. In addition, the growing popularity of mobile data services is also places increasing demands on backhaul. WDM-PON is able to provide symmetrical ultra-high bandwidth to radio base stations and hence can easily address the growing bandwidth needs of mobile backhaul. On the other hand, to shorten the service provision down-time caused by a fibre-failure in a PON, an effective monitoring solution should be applied enabling fault detection and localization. Rapid troubleshooting becomes very important in mobile backhaul systems which support large amount of traffic to/from thousands of users. Centralized and automatic monitoring contributes to operational expenditures (OPEX) savings thanks to remote operation. No hardware upgrade on user side should be required (e.g. demarcation components) due to high hardware and manpower costs per drop link and PON monitoring functionality should be shared over the complete PON system to provide high sharing factor of the investment. Furthermore, the effective fibre-fault detection and localisation scheme should not affect data communication and be sensitive to as low power fluctuations as 1 dB.
Furthermore, operators need to guarantee the level of connection availability specified in the Service Level Agreement, SLA, in particular for business users and mobile backhauling. Protection mechanisms need to be provided in PONs to offer an acceptable reliability level. However, compared with core networks, access networks are very cost-sensitive due to the relatively low sharing factor for the cost associated with the deployment, management and technology upgrade. Therefore, it is important in PON deployment to minimise the cost of protection while maintaining the connection availability at an acceptable level. Furthermore, in order to reduce the affected number of users by single fault which has occurred in fibre access networks, the protection up to Remote Node, RN, needs to be provided in the first place, in particular in a large city with more than one million inhabitants. Due to the ultra dense population in the large city, for the most of access networks the required distance between RN and end user (i.e. the length of drop fibre, DF) is rather short. For instance, in Munich, Germany, the estimated average length of DF per user is less than 1 km (including suburban part). From the reliability point of view, the protection of the feeder fibre might be sufficient for the most cases.